Transcript Catholic University College of Ghana Fiapre

Catholic University College of Ghana
Fiapre-Sunyani
Data Communications and Networks
Internet
INFORMATION TECHNOLOGY II
Audrey Asante, Faculty of ICST
• Computer communication is the transmission of
data and information over a communications
channel between two computers, which can be
several different things.
• Communications between computers can be as
simple as cabling two computers to the same printer.
It can be as complex as a computer at NASA sending
messages through an elaborate system of relays and
satellites to tell a computer on Mars how to drive
around without hitting the rocks.
• Depending on the context, for computer
communications you might use the terms:
•
Data Communications for transmission of data and
information over a communications channel
Telecommunications for any long-distance
communications, especially television
Teleprocessing for accessing computer files located
elsewhere
Communications Channel
• A communications channel, also called a
communications line or link, is the path that
the data follows as it is transmitted from one
computer to another.
COMPUTER NETWORK
• A network is a system of interconnected
computers, telephones, other
communications devices that can
communicate with one another and share
applications and data
NETWORK MODEL
• OSI (Open Systems Interconnect ) Reference
Model
• TCP/IP Reference Model
OSI MODEL
C01. 11
Protocol Architecture Model - OSI
Layer
7
Application
6
Presentation
5
Session
4
Transport
Application Protocol
Presentation Protocol
Session Protocol
Transport Protocol
Application
Presentation
Session
Transport
Communications Subnet Boundary
3
Network
Network
Network
Network
2
Data Link
Data Link
Data Link
Data Link
1
Physical
Physical
Physical
Physical
Host A
INFS 612: Data Communications and Distributed Processing
Host B
J.M. Hanratty
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LAYERS’ FUNCTIONS
Application (Layer 7)
• This layer supports application and end-user processes.
• Communication partners are identified, quality of service is
identified, user authentication and privacy are considered,
and any constraints on data syntax are identified.
• Everything at this layer is application-specific.
• This layer provides application services for file transfers, email, and other network software services.
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LAYERS’ FUNCTIONS
Presentation (Layer 6)
• This layer provides independence from differences in data
representation (e.g., encryption) by translating from
application to network format, and vice versa.
• The presentation layer works to transform data into the form
that the application layer can accept.
• This layer formats and encrypts data to be sent across a
network, providing freedom from compatibility problems. It is
sometimes called the syntax layer.
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LAYERS’ FUNCTIONS
Session (Layer 5)
• This layer establishes, manages and terminates connections
between applications.
• The session layer sets up, coordinates, and terminates
conversations, exchanges, and dialogues between the
applications at each end.
• It deals with session and connection coordination.
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LAYERS’ FUNCTIONS
Transport (Layer 4)
• This layer provides transparent transfer of data between end
systems, or hosts
• The layer is responsible for end-to-end error recovery and
flow control.
• It ensures complete data transfer.
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LAYERS’ FUNCTIONS
Network (Layer 3)
• The layer provides switching and routing technologies
• Creates logical paths, known as virtual circuits, for transmitting data from
node to node
• Provides routing and forwarding functions
• Transforms the Logical Names into Physical Addresses
• Provides internetworking, error handling, congestion control and packet
sequencing.
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LAYERS’ FUNCTIONS
Physical (Layer 1)
• This layer conveys the bit stream - electrical impulse,
light or radio signal -- through the network at the
electrical and mechanical level
• It defines the electrical characteristics of the signals
• It provides the hardware means of sending and
receiving data on a carrier
• It defines Network Interface Cards (NIC), cables, and
connectors
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TYPES OF NETWORKS
• Local network
– It is a privately owned communications network that
serves users within a confined geographical area. The
range is usually within a mile-an office, a building, a
campus. There are two types-private branch exchanges
(PBXs) and Local area networks
• Metropolitan area network
– It is a communications network covering a geographic area
the size of a city or suburb. The purpose is often to bypass
local telephone companies when accessing long-distance
services.
• Wide area network
– It is a communications network that covers a wide
geograhical area, such as a state or a country. The
internet links together hundreds of computer
WANs. Most telephone systems are WANs.
• Global area network
– It is a communications network that covers the
world. An examples is the internet.
Advantages
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Sharing of peripheral devices
Sharing of programs and data
Better communications
Security of information
Access to databases
DISADVANTAGES
• More complexity adds new problems to
handle.
Less customization is possible for shared
programs and folders. Everyone will have to
follow the same conventions for storing and
naming files so others can find the right files.
Sharing is hard for some people
LAN
• They are local networks consisting of a
communications link, network operating
system, microcomputers or workstations,
servers, and other shared hardware.
TYPES OF LAN
• Client/Server LAN
• Peer-to-peer: they don’t rely on a server.
TOPOLOGY OF LANs
• Topology is the logical layout or shape of a
network. The five basic topologies are star,
ring, bus, hybrid, FDDI, Mesh
STAR TOPOLOGY
• All microcomputers and other communication
devices are connected to a central server. If
the server goes down, the entire network will
go off because it handles the flow of
information. The maximum number of
network devices is 1,024 . This configuration is
good for businesses that have large amounts
of rapidly changing data, like banks and airline
reservation . Standard twisted-pair Ethernet
uses a star topology
ADVANTAGES OF STAR TOPOLOGY
• The server prevents collisions between
messages.
• If a connection is broken between any
communications device and the server, the
rest of the devices on the network will
continue operating.
• It's easy to add and remove nodes.
DISADVATANGES OF STAR TOPOLOGY
• They require more cabling than other
topologies
RING TOPOLOGY
• All microcomputers and other communication
devices are connected in a continuous loop.
Each device is connected directly to two other
devices, one on either side of it. There is no
central server. Electronic messages are passed
around the ring until they reach the right
destination. Messages travel around the ring,
with each node reading those messages
addressed to it.
Ring Topology
• The most common type of cabling used for
token ring networks is twisted pair.
Transmission rates are at either 4 or 16
megabits per second
ADVANTAGES OF THE RING TOPOLOGY
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Messages flow in only one direction.
There is no collisions
Requires less cabling.
They offer high bandwidth and can span large
distances
DISADVANTAGES OF RING TOPOLOGY
• If the connection is broken, the entire network
stops working.
• Ring topologies are relatively expensive and
difficult to install
• Moves, adds and changes of devices can affect
the network
• Much slower than an Ethernet network under
normal load
BUS TOPOLOGY
• All communications devices are connected to
a common channel called the bus or
backbone. There is no central server. Each
communications device transmits electronic
messages to other devices. If some of those
messages collide, the device waits and tries to
retransmit. Ethernet 10Base-2 and 10Base-5
networks are bus networks.
Disadvantages
• If a connection in the bus is broken, the entire
network may stop working.
• Extra circuitry and software are needed to
avoid collisions between data
• Can't connect a large number of computers
this way. It's physically difficult to run the one
communications line over a whole building,
for example.
ADVANTAGES OF BUS NETWORK
• It may be organized as a client/server or peerto-peer network
• Any one computer or device being down does
not affect the others.
• Bus networks are relatively inexpensive and
easy to install for small networks.
MIXED/HYBRID TOPOLOGIES
• The purpose of such topologies is to avoid
some of the inconveniencies of the simple
topologies and to use more effectively their
advantages.
• In such topologies, there at least one station,
which belongs to the both topologies. Its role
is to transform the signals and the protocols of
the both networks.
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RING – BUS TOPOLOGY
• An interesting example is the mixed topology,
based on token ring (optical cable) and star
topology is very often used.
• The optical ring can cover more long distances
(between different buildings), and within each
building – the topology can be either star or
bus.
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RING – BUS TOPOLOGY
St.7
St.1
St.2
St.3
St.4
St.6
St.5
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FDDI
• Fiber distributed data interface uses fiberoptic cable with an adaptation of ring
topology using not one but two token rings. It
is costly and fragility because fiber-optic
cables are fragile. It overcomes the
vulnerability by sending data on a clockwise
and a counterclockwise ring:
• in the event of a break data is wrapped back
onto the complementary ring before it
reaches the end of the cable, maintaining a
path to every node along the resulting "C-Ring
• In addition to covering large geographical
areas, FDDI local area networks can support
thousands of users.
ADVANTAGES OF FDDI
• High speed
• Because of the adaptation of two token rings,
if one should fail, the network can continue
operating with the second ring.
MESH TOPOLOGY
This is a network topology in which devices are
connected with many redundant
interconnections between network nodes.
There are two types of mesh topologies:
• full mesh
• partial mesh.
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FULL MESH TOPOLOGY
• Every node has a circuit connecting it to every
other node in a network.
• Very expensive to implement but yields the
greatest amount of redundancy
• If one of those nodes fails, network traffic can
be directed to any of the other nodes.
• Full mesh is usually reserved for backbone
networks
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PARTIAL MESH TOPOLOGY
• Less expensive to implement and yields less
redundancy than full mesh topology.
• With partial mesh, some nodes are organized
in a full mesh scheme but others are only
connected to one or two in the network.
• Partial mesh topology is commonly found in
peripheral networks connected to a full
meshed backbone.
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COMPONENTS OF LAN
• Connection or cabling system: Cabling or
connection system is either wired or wireless.
Wired connections may be done by twistedpair, coaxial or fiber-optic cables. Wireless
connections may be infrared or radio-wave
transmission. Wireless are essential if
computers are portable.
• Transmission media just means the physical
materials that are used to transmit data
between computers.
Twisted wire(phone line)
• Advantage:Easy to string Cheap
Disadvantage:Subject to interference = static
and garble.
attenuation
Fiber optic line (glass fibers)
• Advantage: Smaller
Lighter
Faster (speed of light!)
No interference
• Disadvantage: Expensive
Harder to install and modify
Wireless(infrared, light, radio)
• Advantage: Flexible
Portable
• Disadvantage:Slower data transfer than hardwired methods
Subject to interference
Microwave
• Advantage:Speed of light
Uses a few sites
• Disadvantage: Line-of-sight only
Satellite
• Advantage: Always in sight
• Disadvantage: Expensive uplink and downlink
facilities
Signals
• Two types of signals are used for data
transmission:
Digital and Analog.
• A digital signal is a stream of 0's and 1's. So
this type is particularly appropriate for
computers to use. An analog signal uses
variations (modulations) in a signal to convey
information. It is particularly useful for wave
data like sound waves. Analog signals are what
your normal phone line and sound speakers
use.
Coaxial cable
(round insulated wire)
• Advantage:Not susceptible to interference
Transmits faster
• Disadvantage:Heavy & bulky
Needs booster over distance
• Cross talk
COMPONENTS OF LAN cotn
• Microcomputers with network interface cards.
For communication to go on between two or
more computers, they should have network
interface cards
• Network Operating System: NOS manages the
activities of the network. Example Windows
Server 2003
• Other shared devices: printers, fax, scanners,
peripherals
COMPONENTS OF LAN cotn
• Bridges, routers, and gateways: LANs can be stand alone but
to connect to other networks you can make use of other types
of hardware and software devices as an interface to make
these connections.
• A bridge is a hardware and software combination used to
connect the same types of networks
• A router is a special computer that directs communicating
messages when several networks are connected together.
• A gateway is an interface that enables dissimilar networks to
communicate, such as a LAN with a WAN or two LANs based
on different topologies or network operating systems.
NETWORK SERVERS
• File Server: it is a computer that stores the
programs and data files shared by users on a
LAN.
• It provides global disk space for users which
have certain access and directories
• It organize access rights and allocate resources
to the users
Database Server
• It is a computer in a LAN that stores data.
Unlike a file server, it does not store programs.
PRINT SERVER
• It is a computer in a LAN that controls one or
more printers. It stores the print-image output
to the printer or printers one document at a
time.
• Printer is shared on the network
• They are for cost efficiency since not every
station needs its own printer
COMMUNICATION SERVER
• It handles data exchange with the outside
world as well as internal data exchange
• They usually provide
– Sending and reception of email
– Sending and reception of fax messages
– Connection to the internet
– Connection to other networks
FAX AND MAIL SERVERS
• Fax servers are dedicated to managing fax
transmissions
• Mail servers manage email
BACK UP SERVER
• It is important to backup workstation or server
data.
• They are mainly performed in the nights
INTERNET
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What is Internet
Connecting to the Internet
Internet Addresses
Features of the Internet
INTERNET
• It is the global interconnection of networks.
• TCP/IP is the standardized set of computer
guidelines (protocols) that allow different
computers on different networks to
communicate with each other efficiently.
Connecting to the Internet
• Through school or work
• Online information services
• Internet service providers
INTERNET ADDRESS
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[email protected]
Dasoul:userid
@:separator
Cug.edu.gh: domain
TOP LEVEL DOMAINS
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.com: commercial organizations
.edu: educational and research organizations
.firm
.gov
.info
.org
.int
.mil
.net
SERVICES OF THE INTERNET
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Email
Telnet
File Transfer
Gopher
Chat
World Wide Web (WWW)